Control circuit



Nov. 16, 1948. A. A. MACDONALD qcmnon cmcun um April 19, 1945 [c H 6 U 52.. m ....H.-.

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Patented Nov. 16, 1948 UNITED STATES PATENT OFFICE CONTROL CIRCUIT Angus A. Macdonald, Catonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 19, 1945, Serial No. 589,251 1 8 Claims. 1\

My invention relates to electrical control cir cuits and, in particular, relates to electrical timing circuits.

One object of my invention is to obtain a directcurrent output voltage having an amplitude which is a predetermined function of the time interval separating two voltage pulses impressedon its input terminals.

Another object of my invention is to provide a circuit in which the output voltage is substantially an exponential function of the time interval between the input pulses.

Another object of my invention is to provide a circuit in which the output voltage'is substantially a linear function of the time interval between the input pulses.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings, in which:

Figure 1 is a schematic diagram of a circuit for carrying out the principles of my invention;

Fig. 2 is a graph of curves showing a wave form and timing of voltage pulses impressed on the input terminals of the circuit of Fig. 1 under one condition of operation of that circuit; and

Fig. 3 is a similar graph of the relationship between similar voltage pulses impressed on such input terminals under another condition of operation of my invention.

Referring in particular to Fig. 1, I provide an electrical discharge tube having a cathode and two cooperating electrodes and which is preferably of the high vacuum hot-cathode type well known in the electronic art. A tube having an anode and a control electrode is a well-known example of such a tube. The cathode of the tube I is preferably grounded through a cathode resistor 2, shunted by a capacitor 3 and is likewise connected to one electrode of the tube I through a suitable resistor 4. A voltage pulse e2, having the wave form shown by the lower curve in Figs. 2 and 3, is impressed through a capacitor 5 between ground and this electrode of the tube I. A voltage pulse at, preferably having the wave form of the upper curves shown in Figs. 2 and 3, is impressed between ground and the other electrade of the tube I. A pair of output terminals 8, I are respectively connected across the cathode resistor 2.

As is known in the art, electron discharge tubes change from a relatively non-conductive to a relatively conductive condition when-the voltages impressed between their cathodes and other electrodes are properly related. As a first approximation they are conductive when e1+mez K 2 where m and K are tube parameters. The voltages e1 and e2 are so adjusted to the constants of the tube I that even the maximum value E: of the voltage pulse e2 will be unable to cause current flow through the tube I while e1 has its trough or low value B; and also that even the maximum value E1 of the pulse e1 will be unable to cause current flow when the voltage pulse ea hasits trough or low value D. In other words B-l-mE2 K and E1+mD K. But the value of E2 is made such that e1+mE2ZK whenever e1 exceeds its trough value B. Curves connecting plate voltage and control electrode voltage for electron tubes are well known in the art and will enable those the value E2 before the voltage e1 falls to the trough value B, current will be conducted between the anode and cathode of the tube I, thereby producing a voltage drop in the cathode resistor 2 and charging the capacitor 3. It is obvious that the tube 5 will begin to conduct at the time 111, corresponding to the position of the left-hand edge of the voltage pulse e2, since this is the first time when the voltage e2 has a value at least equal to E2 and the voltage e1 has a value greater than B.

When the tube I hasany substantial conduc tivity its anode-to-cathode resistance will, in eiiect, constitute a resistor through which the capacitor 3 is being charged by the voltage e1.

The value of the anode-to-cathode resistance oftube I obviously depends on the magnitude of the voltages er and ez at the time t1, and by proper design obvious to those skilled in the art, this anode-to-cathode resistance can be made small enough so that the capacitor 3 will charge up almost instantly to the voltage of the source e1 at time '61. Thus, under the conditions illustrated in Fig. 3, the voltage to which the capacitor 3 charges will depend upon the value of the time n and upon the wave shape shown for at in that figure. The voltage to which capacitor 3 charges will increase as the value of the time n decreases.

Once the capacitor 3 has charged up to the value of the voltage e1, current flow through the tube i will cease because, after the time 11, the

s earer.

voltage e1 is smaller than that to which ca pacitor t has just been charged and. m can no longer produce how of charging current through the unilateral conductance of tube i.

If the top portion A-A1 oi the voltage pulse or is made linear, it is obvious that the voltage to which the capacitor ll charges will be proportional to the time interval 131-20. In other words, the capacitor 8 is charged to a voltage which is a linear function of the time interval ti=to just mentioned.

On the other hand, it the top portion .d-A1 oi the voltage pulse or is an eiiponential curve, the voltage to which the capacitor ii charges will be an exponential function of the above-mentioned time interval. Similarly, by altering the wave form of the voltage pulse e1 between the value A and A1 to any other desired curve, the voltage to which capacitor 8 charges can be made any corresponding desired function of the abovementioned time interval.

If the curves er and c2 are non-periodic, i. e. non-repetitive, the capacitor 8 will stay charged to the above-described voltage until it is discharged either by a load impressed across the terminals b, 'i or by lealrage through the resistor t. The higher the value oi the resistor 2, the more slowly the capacitor 3 will discharge under the last-mentioned conditions; and, in particular, by omitting the resistor 2, the capacitor 8 may be lrept charged to the value described in the proceeding paragraph until it is discharged through the load attached to the terminals 7].

n the other hand, it may be desired to make the voltage pulses ex and c2 of a repetitive char actor; that is to say, to give them the form of a series or periodic pulses. in such a case the value of the resistor 2 must be so proportioned to the value of the capacitor as to discharge the latter in a time much greater than the period of repetition.

It will be obvious that the pulse-portions of curve E1 and he may have various forms so long as they conform to the criterion e1+mez K throughout a pulse width corresponding to the desired maximum value oi i'i-in and. also that the portions other than the pulses in those curves may depart from the constant values B, C and D so long as e1+mez is always K. However, by giving the pulses substantially vertical leading (left) edges and making the valves C and D constants, the difilculty or fulfilling the inequalities just mentioned are greatly decreased. It should be noted that my arrangement would still be operative if the voltage of wave shape m were impressed on the grid electrode and er on the anode, but the behavior of the tube would then be more sensitive to unwanted variations of either 81 or en.

It will be noted that in the system so far described the pulse as, having the fiat top, is the later in time than or. If it is desired to obtain an output voltage on the terminals ii, i which decreases instead of increasing with the time intervals tl-t0, the top of the pulse having a non-horizontal wave-top may be sloped upward to the right while the width of the other pulse is made substantially narrower than the former.

The capacitor and resistor d develop a negative bias in a way well known in the art, which insures that discharge will not start in tube i until the positive pulse e: is impressed I claim as my invention:

1. In combination with a grid controlled electrical discharge tube a capacitor connected to be ill Gil)

charged by current how through said tube, means for impressing on the anode of said tube and said capacitor a first voltage pulse, means for impressing on the control electrode of said tube and said capacitor a second voltage pulse, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, one of said voltage pulses having a substantially horizontal crest, and an output circuit connected to derive voltage from said capacitor.

2. In. combination with a grid controlled electrical discharge tube a capacitor connected to be charged by current flow through said tube, means for impressing on the anode of said tube and said capacitor a first voltage pulse, means for impressing on the control electrode of said tube and said capacitor a second voltage pulse, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, both of said voltage pulses having at least one substantially vertical edge, one of said voltage pulses having a substantially horizontal crest, and an output circuit connected to derive voltage from said capacitor.

3. In combination with a grid controlled electrical discharge tube a capacitor connected to be charged by current flow through said tube, means for impressing on the anode of said tube and said capacitor a first voltage pulse, means for impressing on the control electrode of said tube and said capacitor a second voltage pulse, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, both said voltage pulses having substantially vertical edges, one of said voltage pulses having a substantially horizontal crest, and an output circuit connected to derive voltage from said capacitor.

i. In combination with a grid controlled electrical discharge tube a capacitor connected to be charged by current flow through said tube, means for impressing on the anode of said tube and said capacitor a first voltage pulse, means for impressing on the control electrode of said tube and said capacitor a second voltage pulse, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, both of said voltage pulses having substantially vertical edges, one oi said voltage pulses having a substantially horizontal crest, the other said voltage pulse having a substantially rectilinear form between its said vertical edges, and an output circuit connected to derive voltage from. said capacitor.

5. In combination with a grid controlled electrical discharge tube a capacitor connected to be charged by current flow through said tube, means for impressing on the anode of said tube and. said capacitor'a first voltage pulse, means ior impressing on. the control electrode of said tube and said capacitor a second voltage pulse, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, both said voltage pulses having substantially vertical edges, one of said voltage pulses having a substantially horizontal crest, the other said pulse having a substantially exponential portion between its said vertical edges, and an output circuit connected to derive voltage from said capacitor.

6. In combination with a load circuit on which it is desired to produce a voltage which varies as a predetermined function of. a time interval, a capacitor connected across said circuit, an electrical discharge tube having a cathode and two voltage pulses having a substantially vertical edge portion, one of said voltage pulses having a substantially horizontal crest during said overlap and the other said voltage pulse having a form during said overlap which varies in accordance with said function.

7. The method of deriving a voltage pulse which is a predetermined function of a time interval which comprises charging a capacitor through a tube having at least three cooperating electrodes, impressing between one pair of said electrodes a voltage in the form of a pulse having a substantially horizontal crest, impressing between another pair of said electrodes a voltage pulse having a pair of substantially vertical edges connected by a time curve which corresponds to said predetermined function, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses. and caus-' ing said voltage pulses to overlap in time by an amount corresponding to said time interval.

8. In combination a capacitor, an electron tube having two electrodes cooperating with a cathode which is connected to one terminal of said capacitor, and means for impressing between one of said electrodes and the other terminal of said capacitor a voltage pulse having a substantially vertical edge and a horizontal crest, means for impressing between the other said electrode and said other terminal of said capacitor a voltage pulse having a substantially vertical edge adjoin ing a rectilinear top, said capacitor being intended to be charged in an amount dependent upon the overlap in time of said pulses, and

means for causing an overlap in time predeterminable at will between said voltage pulses.

' ANGUS A. MACDONALD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 1 Date 2,250,708 Herz July 29, 1941 2,287,174 Heising June 23, 1942 2,335,265 Dodington Nov. 30, 1943 

